Since the cured product of a curable resin composition formed of an epoxy resin and a curing agent thereof has excellent heat resistance, moisture resistance, and insulating properties, the curable resin composition is widely used as a sealant for a semiconductor or an insulating material for a printed wiring board.
Among these, in printed wiring board applications, with a trend of miniaturization or performance enhancement of electronic devices, realization of a high density wiring by narrowing a wiring pitch has been demanded, and as a semiconductor mounting method corresponding thereto, instead of the wire bonding method in the related art, a flip chip connection method of bonding a semiconductor device and a wiring board by solder balls has become a mainstream. In the flip chip connection method, solder balls are placed between a wiring board and a semiconductor, a wiring board and a semiconductor are bonded by heating the whole to reflow the solder, and thus, a wiring board insulating material having higher heat resistance has been demanded. At the same time as this, with technological innovations such as increase in speed and frequency of signals in electronic device, and exclusion of a halogen-based flame retardant, a resin material capable of realizing further reduction in a dielectric constant and dielectric tangent and high flame retardancy even in a halogen-free state has been demanded.
A technology for using an active ester compound obtained by esterifying a dicyclopentadiene phenolic resin and α-naphthol with isophthalic acid chloride as a material capable of realizing a low dielectric constant and a low dielectric tangent, as a curing agent for an epoxy resin, is known (refer to PTL 1). An epoxy resin composition using the active ester compound described in PTL 1 is a composition successful in reducing both the dielectric constant and the dielectric tangent compared to the case of using a phenol novolak-type active ester resin known in the related art. However, such an active ester compound has a dicyclopentadiene skeleton in the molecular structure, and thus, the cured product is likely to burn, and does not have sufficient heat resistance.